Positive-mode photographic process and composition

ABSTRACT

A positive-mode photographic process, and composition therefor, wherein an organic photo-sensitive polymer-former and dye progenitor are dispersed in a non-solubilizing hydrophilic vehicle. Exposure forms a latent image by polymerization in light struck areas. A visible, positive image is obtained by developing the dye progenitor in non-polymerized areas. Multi-layers can be provided with substractive color-dye progenitors to yield a full color direct positive print.

United States Patent Yamada et al.

[4 1 Mar. 21, 1972 POSITIVE-MODE PHOTOGRAPHIC PROCESS AND COMPOSITION Inventors: Yoshikazu Yamada, Sierra Madre; Thomas H. Garland, El Monte, both of Calif.

Assignee: Bell & Howell Company Filed: July 29, 1968 Appl. No.: 748,420

Related US. Application Data Continuation-in-part of Ser. No. 523,705, Jan. 28, 1966, Pat. No. 3,503,745, which is a continuation-inpart of Ser. No. 481,759, Aug. 23, 1965, Pat. No. 3,476,562, which is a continuation in-part of Ser. No. 352,625, Mar. 17, 1964, abandoned, which is a continuation-in-part of Ser. No. 278,050, May 6, 1963, abandoned.

US. Cl. ..96/90 R, 96/115 P, 96/48 R Int. Cl ..G03c 1/52 Field of Search ..96/90, 1 15 P Primary ExaminerNorman G. Torchin Assistant Examiner-John Winkelman AtlorneyNilsson, Robbins, Wills & Berliner [57] ABSTRACT A positive-mode photographic process, and composition therefor, wherein an organic photo-sensitive polymer-former and dye progenitor are dispersed in a non-solubilizing hydrophilic vehicle. Exposure forms a latent image by polymerization in light struck areas. A visible, positive image is obtained by developing the dye progenitor in non-polymerized areas.

' Multi-layers can be provided with substractive color-dye Y progenitors to yield a full color direct positive print.

15 Claims, 4 Drawing Figures Patented March 21, 1972 /MA Gl/VG K m E H INVENTORS, yaw/x420 YAMA 0A, man fl. GAELA/VO Mum/Y 4" [Md/Mr POSITIVE-MODE PHOTOGRAPHIC PROCESS AND COMPOSITION CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 523,705, filed Jan. 28, 1966, now US. Pat. No. 3,503,745 issued Mar. 31, 1970 which in turn is a continuation-in-part of application Ser. No. 481,759, filed Aug. 23, 1965, now US. Pat. No. 3,476,562, issued Nov. 4, 1969, which in turn is a continuation-in-part of application Ser. No. 352,625 filed Mar. 17, 1964, now abandoned which in turn is a continuation-in-part of application Ser. No. 278,050, filed May 6, 1963, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The field of art to which the invention pertains includes the field of photographic chemistry, processes and materials, particularly light sensitive compositions involving dyes and dyeformers.

2. Description of the Prior Art A variety of organic photosensitive systems are known in the art and generally involve two or more organic materials which react under the influence of actinic light to produce a color. As early as 1921, Murray C. Beebe and his co-workers described numerous organic photographic systems utilizing halogen compounds in combination with a second ingredient (e.g., US. Pat. Nos. 1,574,357, 1,574,358, 1,574,359, 1,575,143, 1,583,519, 1,587,269, 1,587,270, 1,587,271, 1,587,272, 1,587,273, 1,587,274, 1,604,674, 1,618,505, 1,655,127, 1,658,510 and 1,820,593). It has been theorized that light effects the release ofa radical from the halogen compound which carries out a color-forming reaction with the second compound. Subsequent workers such as Eugene Wainer and Sprague (e.g., US. Pat. Nos., 3,042,515, 3,042,516, 3,042,517, 3,042,518, 3,042,519, 3,046,125 and 3,056,673) as well as a number of other workers, have continued the development of various photographic systems involving a photo-activated reaction of a combination of a halogen containing compound and one or more other compounds. Other recent disclosures include British Pat. No. 917,919 and Belgium Pat. No. 516,094.

More recently, it has been discovered that some of the above combinations can be advantageously dispersed in a continuous phase in which the combinations are substantially insoluble (e.g., gelatin or other similar aqueous support). The result is a photographic composition of superior speed and, with certain reactants, a ready ability to yield a positive print. In this latter mode, a component is provided, e.g., N-vinylcarbazole, which can either polymerize or form a color depending on the intensity of exposure. The initial, image-wise exposure causes polymerization and consequent desensitization. Subsequent blanket exposure with more intense light causes color formation in areas of the film not previously exposed. This discovery has been described in our applications, Ser. Nos. 278,050 and 481,759, noted above.

Typically, the foregoing photo-systems rely on color formation by one of two principal ingredients. For example, in some of the aforementioned Wainer patents, a N-vinyl compound (US. Pat. No. 3,042,517) or dye base (US. Pat. No. 3,095,303) in combination with an organic halogen compound forms a color upon exposure to light. Even the aforementioned positive-mode process obtains its color with unreacted N-vinyl compound and organic halogen. None of the foregoing processes can yield positive-mode prints with a wide choice of colors; none of them can yield full-color positive mode prints.

SUMMARY OF THE INVENTION The present invention provides a positive-mode photographic process that will allow a wide choice of colors and is capable of yielding full-color prints, In an important embodiment, multi-layers of photosensitive material are provided,

each layer having a different spectral response and yielding a different color when developed.

In another-embodiment, we provide photosensitive material comprising: a photosensitive polymer-forming composition; an optical sensitizer for the polymer-forming composition; and a dye progenitor that is different from any polymer-forming component of the composition and is responsive to electromagnetic radiation to yield a color. The composition is image-wise exposed to light to form a latent image which is obtained by polymerization in light struck portions of the material. The image is developed by exposure to electromagnetic radiation of sufficient intensity and duration to yield color from the dye progenitor in non-polymerized portions. The polymer-forming composition preferably comprises an organic photo-initiator and an N-vinyl compound.

In still another embodiment, the photosensitive material comprises a photo-initiator, an N-vinyl compound, an optical sensitizer and a dye progenitor that is responsive to chemical development to yield a color. After image-wise exposure and formation of. a latent image by polymerization, color is obtained in non-polymerized areas by contacting the material with a developing agent for the dye progenitor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic perspective view of a multilayered film of this invention during exposure;

FIG. 2 is a diagrammatic, perspective view of the film of FIG. 1 being developed by light;

FIG. 3 is adiagrammatic, perspective view of the film of FIG. I and 2 following color development; and

FIG. 4 is a diagrammatic perspective view of the film of FIG. 1 being chemically developed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, in one embodiment of this invention, a film 10 is provided with a paper backing l2 and three layers 14, 16 and 18 of photosensitive material as hereinafter described. Each layer comprises a photosensitive polymerforming composition and a dye progenitor in a suitable binder. In this case, each layer comprises a gelatin dispersion of N- vinylcarbazole and carbon tetrabromide. Such formulation, among others, are described in detail in our above-noted U.S. Pat. No. 3,476,562. A different optical sensitizer and dye progenitor is contained in each layer. The dye progenitors are dye bases selected to each yield one of the primary colors on formation of the dye, to provide a subtractive color system. Thus, the lowermost layer 14 can contain an optical sensitizer that absorbs red light and a dye base that yields a cyan color on generation of the dye form. The middle layer 16 can contain an optical sensitizer that absorbs green light and a dye base that yields a magenta color upon dye generation. The uppermost layer 18 can contain an optical sensitizer that absorbs blue light and a dye base that yields a yellow color upon generation of the dye form. Additionally, the uppermost layer advantageously contains a yellow filtering material to absorb substantially all of the blue light to prevent its activation of lower layers. The filter can also be located just below the top layer 18 as is known in silver halide photochemistry.

A wide variety of dye bases are known to the art, e.g., see the above noted US. Pat. No. 3,095,303 as well as US. Pat. Nos. 3,100,703 and 3,102,810 and F. M. Hamer The Cyanine Dyes and Related Compounds, pages 351-374 and 344-346. Interscience Publishers, New York (1964). As particular examples, about 0.2 weight per cent (of the gelatin) of each of Z-(p-dimethylaminostyryl)benzimidazole, 2-[3-(3- ethyl-2(3H)-benzoxazolylidene)-propenyl]-quinoline and 4- 1-cyano-5-( 3-ethyl-2( 3H )-benzoxazolylidene )-1 ,3-pentadienyl]- quinoline can be added as dye bases to the bottom 14, center 16 and top 18 layers, respectively.

For other examples of suitable dye progenitors, reference can be made to our earlier US. Pat. No. 3,503,745 and to a 1957 publication of Brooker and Vittun entitled A Century of Progress in the Synthesis of Dyes for Photography" in the Journal of Photographic Science, Volume 5, 1957 pages 71-78, the disclosure of such publication being incorporated herein by reference. Illustrative materials are: bases of which cyanines, hemicyanines and thiacyanines are quaternary salts; styryl dye bases and their higher vinylene analogs; weakly colored merocyanine dyes as disclosed in US. Pat. No. 3,l06,466; and leuco triphenylmethane dyes.

Cyanine bases and compounds having a styryl substituent such as the styryl dye bases are particularly useful in our invention and comprise a particularly preferred group of dye progenitors.

Although various of the foregoing dye progenitors have been described in our noted previous applications, their ability to form a color was not critical to their use in such applications. In the present invention a color-forming amount, rather than merely a sensitizing amount of the dye base is utilized, which color-forming amount generally may range from about I milligram to about 0.1 grams per gram of polymer-forming material.

A large number of optical sensitizers are also well known to the art, e.g., see P. Glafkides Photographic Chemistry, Volume 2, pages 564-566, Fountain Press, London, (1960). About 0.05 weight per cent (of the polymer-former) of chloroquino-dimethylbenzthiacarbocyanine ethiodide can be added as a red optical sensitizer to the bottom layer 14 and about 0.05 weight per cent of mesoethyl-phenyloxacarbocyanine propyl nitrate can be added as a green optical sensitizer to the center 16. The top layer 18 is generally sufficiently blue-light sensitive as to not require an optical sensitizer; however, for emulsions which are not sufficiently bluelight sensitive, about 0.04 weight per cent of methyl orange can be added to the top layer 18. Additionally, the top layer 18 can contain tartrazine dye as a yellow filter.

The concentration of the optical sensitizers should generally be greater for lower layers, to compensate for decreases in light intensity as the light is filtered. Changes in the relative sensitivity of the layers can also be made to balance for expected lighting conditions as is done with silver halide films.

The film is image-wise" exposed to light projection through a full color transparency 20 including, in this case, a red portion 22, a blue portion 24, and a green portion 26. The imaging light is projected by a conventional source 28 of visible actinic light which in this instance is a tungsten lamp (indicated diagrammatically).

The actinic light from the source 28 is selectively absorbed by transparency 20 with red, blue and green light being transmitted by the red 22, blue 24 and green 26 portions, respectively. Referring specifically to the transmitted red light, it passes through the upper 18 and middle 16 film layers and is absorbed by the red optical sensitizer in lowermost layer 14. Absorption of the light initiates polymerization of the photosensitive polymer-former in that layer 14. With the aforementioned components, it is believed that the absorbed light effects the release of a free radical,ion or radical ion which, at these levels of exposure, causes the N-vinylcarbazole to form a colorless polymer 30. Polymerization can be aided by the application of heat from a heater 32 underlying the paper backing and operative during and/or after the exposure period. The level ofimage-wise" exposure is not sufficient to cause the dye base in that layer to react to any significant extent with the light generated free-radical or ion but is sufficient to cause the above described polymerization.

The transmitted red light passes through the upper layer 18 and the middle layer 16 without significant absorption by the optical sensitizers in these layers. The light transmitted through the blue portion 24 of the transparency 20 is absorbed, through the action of the optical sensitizer in the uppermost layer 18. The yellow filter thereat prevents any further propagation of the blue light. Similarly, light transmitted through the green transparency portion 26 is absorbed, through the action of the optical sensitizer in the middle layer 16. Polymerization in these layers occurs to form polymer 34 and 36 in the upper 18 and middle 16 layers, respectively.

It is believed that the polymer formation involves a chaintype reaction that both decreases the supply of carbon tetrabromide initiator to render the exposed portions much less sensitive to further light exposure and effectively encapsulates" the chemical components in the polymerized portion, isolating them and preventing their contact. In one embodiment, aqueous solutions are utilized to chemically develop image color. Here, the effective encapsulation" of components prevents color development in those areas by preventing contact with the aqueous solutions. The film 10 is still photosensitive in portions that were not light struck in the initial, image-wise, exposure; thus, a latent image is present, defined by the polymerized portions, 30, 34 and 36 of the film 10.

Referring to FIG. 2, one method of developing color is shown. The film 10 is subjected to a blanket or overall exposure to light from a relatively strong light source 38 (not necessarily strong as a light source, but stronger than the image-wise exposure) and concurrently and/or subsequently heated by a heater 40 to effect a conversion of the dye bases to the corresponding dyes. (The use of a heater is optional to hasten color development.) Thus, the dye bases in the nonimage portions 42, 44 and 46 of the lower 14, middle 16 and upper 18 layers, respectively, form a cyan, magenta and yellow color, respectively.

FIG. 3 depicts the resultant film. Looking through the layers, a red color 48 is seen where the magenta 44 and yellow 46 portions overlap. A blue color 50 is seen where the cyan 42 and magenta 44 portions overlap. Similarly, a green color 52 is seen where the cyan 42 and yellow 46 portions overlap.

The foregoing selective polymerization involves a positiveworking mode of reaction and such modes are described in our earlier noted applications. In the environment of a nonsolubilizing, aqueous continuous phase, the combination of the organic halogen compound and the N-vinyl compound is apparently capable of undergoing two separate and distinct reactions upon exposure to actinic light. With very weak light, a colorless polymer is thought to be formed which desensitizes that portion to subsequent color formation. With moderately strong light, the N-vinyl compound reacts to form a color. With the present formulation, there is also a relatively fast dye forming reaction between the aforementioned radical or ion, or radical ion and dye base. Thus, in the initially light struck areas, at 30, 34 and 36, three reactions are apparently competitive, the kinetics of which say that one or the other will predominate depending on the intensity of light, exposure time and/or wavelength of light. The colorless polymer forming reaction occurs with weaker light, i.e., lower levels of light wherein the intensity is less and/or the exposure times are shorter as such weak light is obtained from the imaging light source 28 (FIG. 1). The reaction converting the dye-base to the dye occurs with stronger" light, as from the blanketing light source 38 (FIG. 2), and predominates over the N-vinyl compound color reaction which requires still stronger exposures.

The following example illustrates color formation by means of the sequence of FIGS. 1,2 and 3.

EXAMPLE 1 A sheet of baryta-coated paper is sequentially coated to about 10 mil wet thickness each with emulsions A, B and C of the following formulations, each coating being dried before application of the succeeding coating:

All N-vinylcarbazole' 4 grams All carbon tetrabromide' 3.2 grams Emulsion A 2-(p-dimethylaminostyryl)- benzimidazole 0.1 gram complex merocyanine: 0.002 gram lepidine-t-dimethylbenzoxazole Emulsion B 2-[3-(3 ethyl-2(3H)-benzoxazolylidoneypropenyl]- quinoline 0.1 gram dichlorimidazoleselenacarbocyanine (acetoxypropylthiocyanate) 0.002 gram Emulsion C 4-[ l-cyano 5-(3-ethyl-2(3H)- -benzoxazolylidene)-l ,3-pentadienyl]-quinoline 0.1 gram tartrazine dye 0.002 gram added together in 2 ml. of ethyl acetate The composition is blue sensitive without a sensitizer therefor; the tartrazine dye serves as a filter for lower layers.

Each emulsion is prepared by admixing the ingredients and blending with violent agitation in a Waring blender or other high shear mixer. The Dow Corning Anti-Foam B is to prevent foaming during preparation. The formalin is to harden the gelatin.

The dried sheet is exposed for seconds to an 8-diameter Kodachrome projection imaged from a 300 watt Bell & Howell Headliner slide projector at 34 inches. The sheet is then warmed for about 10 seconds on a rotating drum heater at about 70 C. and then exposed to ordinary fluorescent room light to print out a positive full color image.

In place of the foregoing dye progenitors, one can use similar amounts of: 2-[3-( l-ethyl-2( lI-I)-quino-lylidene) propenyll-benzothiazole or 4-[3'(3-ethyl-2(3I-I)- benzothiozolylidene) -propenyl]-quinoline to yield a cyan color; 4-(p-dimethylaminostyryl)-quinoline or 4-[cyano-2-(pdimethylaminostyryl) ]-quinoline to yield a magenta color; and 2-[(3-ethyl-2(3H)-benzothiazolylidene) -ethylidene]- aminobenzothiazole or 4-[5-(3-ethyl)-2(2H)-benzothiazolylidene-l ,3-pentadienyll-quinoline to yield a yellow color. 7

In place of the foregoing optical sensitizers, one can use similar amounts of: complex merocyanine: methylethoxybenzthiazole diphenylthiazole, or complex merocyanine: hydronaphthothiazole diphenylthiazole as the red sensitizer; and mesoethyl-phenyloxadimethylthiacarbocyanine (ethyl percholorate) or mesoethyl-phenyloxacarbocyanine (ethyl thiocyanate) as the green sensitizer. As a yellow filter one could utilizer yellow colloidal silver (although one would not then achieve an entirely organic system), or new coccine, or pure yellow F40.

The foregoing photographic procedures involve dry processes; that is, no liquid development is needed. In such cases, any of a variety of photosensitive polymer-forming materials may be used. Thus, the N-vinylcarbazole can be replaced with other N-vinyl compounds such as N-vinylphthalimide, N-vinylindole, N-vinylpyrrole, or N-vinyltetrahydrocarbazole. .A completely different type of polymerformer can be used, such as acrylates or vinyl ethers; however, the N-vinyl compounds are generally preferred as more reliable than other polymer-formers. A concentration of polymerformer in the binder can vary from as low as 10 weight per cent to as high as 50 weight per cent.

The photo-initiator is generally a compound which produces, or complexes to produce, free radicals or ions, or radical ions upon exposure to light of a suitable wavelength, and which can react with the dye base. Examples include the haloalkanes, halomethylnaphthalenes, haloketones,

halogenated acids, sulfonyl halides and aroyl peroxides. Suchof these materials as are discussed by McCloskey and Bondin Industrial Engineering Chemistry, Volume 47, page 2,125 et seq. (1955) are of interest here, and such disclosure is incorporated herein by reference.

In general, it is preferred that the photo-initiator be an organic halogen compound as these have been found to be the most effective. Such compounds are described in detail in our earlier U.S. Pat. No. 3,476,562. In general, organic halogen compounds are preferred in which there is present at least one active halogen selected from the group consisting of chlorine, bromine and iodine, attached to a carbon atom having not more than one hydrogen atom attached thereto. Examples of such compounds include dibromodichloromethane, bromotrichloromethane, tribromomethyl-Z-methyl 2- propanol. Others can be found in our noted earlier application and also in certain patents issued to Eugene Wainer and Robert Sprague such as U.S. Pat. Nos. 3,042,515, 3,042,516, 3,042,517, 3,042,518, 3,042,519, 3,046,125, 3,056,673 and 3,082,086, the disclosures of such patents being incorporated herein by reference.

In a particular embodiment of this invention, it is preferred to use as an initiator an organic halogen compound having the formula Br-C--(X) (X') (X")n(CY l-n where X,X' and X" are halogens, each Y is independently selected from the group consisting of halogen, hydrogen, hydroxy,methyl, and methylol, and n is selected from O and 1, such that when n is 0,X and X are Br. These compounds are generally more compatible and more effective with the styryl and cyanine dye bases, and are preferred in such combination. Examples of such compounds and combinations can be found in the above-identified patents to Wainer and Sprague and in our prior applications A suitable concentration of photo-initiator depends on the particular polymer-former and dye progenitor, but generally a weight ratio of polymer-former to photo-initiator of from about 1:1 to about 5:1 is satisfactory.

When an N-vinyl compound is used as the polymer-former, the polymer resulting from light exposure is generally impervious to water penetration and thereby allows liquid development of the unexposed portions of the film. Referring to FIG 4, such an alternative method of development is shown. Rather than being light developed as in FIGS. 2 and 3', the film 10 is immersed in a tank 54 containing an aqueous solution of reagent 56 for the dye bases, which converts them to the corresponding dyes. The nature of the reagent depends on the nature of the dye bases utilized. Styryl and cyanine dye bases may be protonated (acidified) or quarternized to the dye form, whereas leuco triphenylmethanes are oxidized and acidified to the desired color. A 3 weight per cent solution of H 0 ceric salts, persulfates, or the like, can be utilized.

The polymerized, imaged portions 30, 34 and 36 of the film 10 are impervious to the aqueous solution 56, whereas the unimaged portions 42, 44 and 46 are wettable by the solution 56 to permit the dye bases to be oxidized or protonated to their corresponding dye colored forms. The resultant film is similar in appearance to the developed film of FIG. 3, showing red 58, blue 60 and cyan 62 portions.

In place of the foregoing dye bases and leuco dyes, one could utilize any of the well known color couplers and oxidized developers used for a similar purpose in silver halide photochemistry. The following example illustrates the use of such couplers.

EXAMPLE 2 A baryta-coated sheet is sequentially coated, as in Example 1, with the following formulations, prepared as in Example I:

All carbon tetrabromide 3.2 grams Emulsion A pinacyanole 0.002 gram Emulsion A ,B-chloro-a-naphthol 0,l gram Emulsion B 4-(p-dimethylaminostyryl)- quinoline 0.002 gram Emulsion B l-phenyl-3-methyl-5-pyrazolone O.l gram Emulsion t'. acctoacet-2,5-dichloroanilide 0.1 gram added together in 2 ml. of ethyl acetate The composition is blue sensitive without a sensitizer therefor.

The dried sheet is exposed and heated as in Example 1, processed by immersion into an aqueous solution of 4 weight per cent 4-amino-N-ethyl N-(B-methylsulfonamido-ethyl)mtoluidine in alkaline (pH solution, followed by an aqueous solution of 5 weight per cent ammonium persulphate, as oxidizing agent, and then rinsed to yield a positive full color image.

The concentration of color coupler is generally of the same range as that for the dye progenitor. The decreased amount of dye base is present, not for its color forming properties, but for its optical sensitizing properties. Accordingly, a sensitizing, rather than color forming, amount is used. Generally, from about 0.1 to about l0 milligram of sensitizer per gram of polymerformer is satisfactory. Other optical sensitizers can be used in their place, and can be selected from those described above.

In a further embodiment of this invention, the polymerforming material is particulate, that is in the form of particles, generally of from about 0.5- microns diameter. Preferably, the material is dispersed in a substantially non-solubilizing continuous phase, which is generally water-penetrable. Such dispersions are particularly well-suited for development in accordance with our processes. The solid-film-forming component used to achieve the continuous phase may be any ofa number of generally photographically inert materials, which are, in most cases, soluble in water or so finely dispersible therein in the concentrations of use that for practical purposes there is no distinction between solution and dispersion for these materials in the continuous phase. Such materials include the starch and starch derivatives, proteins, (i.e., casein, zein, gelatin, thiolated gelatin, etc.), alginates, gums and the like materials which are generally considered to be natural derivatives of natural film-forming materials, any one of which in its conventional water soluble" form is useable in films of the instant invention. In addition synthetic water-soluble filmformers are particularly suitable binders for photosystems of this invention and such materials include polyvinyl alcohol, various commercially available amine or amine-aldehyde resins, etc. Also, a number of cellulose derivative film-formers may be used, and these include the various water-soluble cellulose ethers, carboxymethyl-cellulose, hydroxypropylmethylcellulose, etc. Essentially these materials are photo-insensitive and their principal function is that of forming the desired film to retain the dispersed phase in discrete particle form. Of the above materials, gelatin, casein, polyvinyl alcohol, gum arabic, starch, alkali metal carboxymethylcellulose (e.g., sodium carboxymethylcellulose) and hydroxyethylcellulose are particularly useful in this invention.

Use of the above-described type of non-solubilizing continuous phase as support for organic photochemical materials yields particularly good results with our processes and are particularly preferred where an N-vinyl compound is used as an image-yielding material, particularly in conjunction with an organic halogen compound. Such photosystems are described in detail in our earlier applications, as noted above, particularly in application Ser. No. 481,759, now US. Pat. No. 3,476,562 and the disclosure in Ser. No. 481,759 is incorporated herein.

While the present inventive concepts have been described with respect to multilayered films, they have equal applicability to single-layered films where normally negative-working systems are thereby converted to positive-working systems. In

our previous applications, and in the work of others, color formation occurred with the same material that formed the polymer. Marked improvements in color rendition can be obtained and a wide variety of colors can be made available by using the present methods with just a single emulsion layer. The following examples illustrate single-layered films of this invention.

EXAMPLE 3 A sheet of baryta-coated paper is coated as in Example 1 with the following formulation, prepared as in Example 1:

Component Amount gelatin I0 grams water 36 ml. N-vinylcarbazole 5 grams carbon tetrabromide 1 gram Dow Corning Anti-Foam B 6 drops formalin I drop leuco crystal violet 0.] grams A dried sheet is exposed and heated as in Example 1 and then exposed to room light, with a resultant positive violet image.

EXAMPLE 4 The formulation and coating operation of Example 3 is repeated except that leuco malachite green is substituted for the leuco crystal violet. A dried sheet is exposed as in Example 1 but for 10 seconds, warmed at about C. for about 10 seconds, and then brought out into room light. A positive, malachite green image is obtained.

EXAMPLE 5 The formulation and coating operation of Example 3 is repeated except that 4-(p-dimethylaminostyryl)-quinoline is substituted for the leuco crystal violet. A dried sheet is exposed and heated as in Example 1 and then brought out into room light to yield a positive pink image.

EXAMPLE 6 A vellum sheet is coated as in Example 1 with the following formulation prepared as in Example 1:

The Triton X-lOO is a wetting agent. The dried sheet is exposed as in Example 1, but for 10 minutes, warmed at 70 C., for about 10 seconds and then exposed to room light to yield a pink-positive image.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of this invention.

What is claimed is:

1. A photographic process comprising:

providing photosensitive material dispersed in a non-solubilizing hydrophilic vehicle, said material comprising a photosensitive polymer-forming composition, and a dye progenitor differing from any polymer-forming component of said composition and capable of modification by electromagnetic radiation to a color form;

determining a first level of light exposure sufficient to cause polymerization of said polymer-forming composition but insufficient to substantially radiatively modify said dye progenitor to a color form; f

image-wise exposing said material to said first level of lig h whereby to form a latent image defined by polymerization in light-struck portions of said material; and

developing said material by exposure to electromagnetic radiation of sufficient intensity and duration to radiatively modify said dye progenitor to form a color in nonpolymerized portions. 2. The process of claim 1 wherein said material comprises at least two layers, each containing a sensitizing small amount of optical sensitizer to broaden its spectral response, said layers having differing spectral responses and yielding differing colors when developed.

3. A photographic process comprising: providing a photosensitive composition dispersed in a nonsolubilizing hydrophilic vehicle, said composition comprising a photo-initiator, an N-vinyl compound, and a dye progenitor differing from said N-vinyl compound, in an amount sufficient to form a color when developed;

determining a first level of light exposure sufficient to cause polymerization of said N-vinyl compound but insufficient to substantially radiatively modify said dye progenitor to a color form;

image-wise exposing said composition to said first level of light whereby to form a latent image defined by polymerization of said N-vinyl compound in light-struck portions of said composition; and

developing said composition to form color from said dye progenitor in non-polymerized portions.

4. The process of claim 3 wherein said composition contains a sensitizing small amount of an optical sensitizer to broaden spectral response.

5. The process of claim 4 wherein said composition comprises at least two layers of differing spectral response and yielding differing colors when developed.

6. The process of claim 3 wherein said dye progenitor is a dye in base form.

7. The process of claim 3 wherein said photoinitiator is an organic halogen compound.

8. The process of claim 3 wherein said N-vinyl compound is N-vinylcarbazole.

9. The process of claim 3 wherein said dye progenitor is capable of modification by electromagnetic radiation to a color form and the composition is developed following said latent image formation by exposure to electromagnetic radiation of sufficient intensity and duration to radiatively modify said dye progenitor to a color form in said non-polymerized portions.

10. The process of claim 3 wherein said dye progenitor is responsive to chemical development to yield a color and developing said composition comprises contacting said composition with a chemical for said development.

11. The process of claim 3 wherein the weight ratio of N- vinyl compound to photo-initiator is from about 1:1 to about 5:1 and the weight ratio of N-vinyl compound to dye progenitor is from about 1:0.00l to about 1:0.].

12. Photosensitive material comprising:

a photo-initiator;

an N-vinyl compound; and

a dye progenitor differing from said N-vinyl compound and capable of modification by chemical development to yield a color, said dye progenitor being present in an amount sufficient to form a color when developed;

said initiator, N-vinyl compound and dye progenitor being dispersed in a non-solubilizing hydrophilic vehicle.

13. The photosensitive material of claim 12 wherein said photo-initiator is an organic halogen compound.

14. The photosensitive material of claim 12 formed into at least two layers, each containing a small sensitizing amount of optical sensitizer to broaden its spectral response, said layers having differing spectral responses and yielding differing colors when developed.

15. The photosensitive material of claim 12 wherein the weight ratio of N-vinyl compound to photo-initiator is from about 1:1 to about 5:1 and the weight ratio of N-vinyl compound to dye progenitor is from about 110.001 to about 1:0.]. 

2. The process of claim 1 wherein said material comprises at least two layers, each containing a sensitizing small amount of optical sensitizer to broaden its spectral response, said layers having differing spectral responses and yielding differing colors when developed.
 3. A photographic process comprising: providing a photosensitive composition dispersed in a non-solubilizing hydrophilic vehicle, said composition comprising a photo-initiator, an N-vinyl compound, and a dye progenitor differing from said N-vinyl compound, in an amount sufficient to form a color when developed; determining a first level of light exposure sufficient to cause polymerization of said N-vinyl compound but insufficient to substantially radiatively modify said dye progenitor to a color form; image-wIse exposing said composition to said first level of light whereby to form a latent image defined by polymerization of said N-vinyl compound in light-struck portions of said composition; and developing said composition to form color from said dye progenitor in non-polymerized portions.
 4. The process of claim 3 wherein said composition contains a sensitizing small amount of an optical sensitizer to broaden spectral response.
 5. The process of claim 4 wherein said composition comprises at least two layers of differing spectral response and yielding differing colors when developed.
 6. The process of claim 3 wherein said dye progenitor is a dye in base form.
 7. The process of claim 3 wherein said photoinitiator is an organic halogen compound.
 8. The process of claim 3 wherein said N-vinyl compound is N-vinylcarbazole.
 9. The process of claim 3 wherein said dye progenitor is capable of modification by electromagnetic radiation to a color form and the composition is developed following said latent image formation by exposure to electromagnetic radiation of sufficient intensity and duration to radiatively modify said dye progenitor to a color form in said non-polymerized portions.
 10. The process of claim 3 wherein said dye progenitor is responsive to chemical development to yield a color and developing said composition comprises contacting said composition with a chemical for said development.
 11. The process of claim 3 wherein the weight ratio of N-vinyl compound to photo-initiator is from about 1:1 to about 5:1 and the weight ratio of N-vinyl compound to dye progenitor is from about 1:0.001 to about 1:0.1.
 12. Photosensitive material comprising: a photo-initiator; an N-vinyl compound; and a dye progenitor differing from said N-vinyl compound and capable of modification by chemical development to yield a color, said dye progenitor being present in an amount sufficient to form a color when developed; said initiator, N-vinyl compound and dye progenitor being dispersed in a non-solubilizing hydrophilic vehicle.
 13. The photosensitive material of claim 12 wherein said photo-initiator is an organic halogen compound.
 14. The photosensitive material of claim 12 formed into at least two layers, each containing a small sensitizing amount of optical sensitizer to broaden its spectral response, said layers having differing spectral responses and yielding differing colors when developed.
 15. The photosensitive material of claim 12 wherein the weight ratio of N-vinyl compound to photo-initiator is from about 1:1 to about 5:1 and the weight ratio of N-vinyl compound to dye progenitor is from about 1:0.001 to about 1:0.1. 